The present invention relates to a sealing arrangement for a suction box of a suction roll comprising a fixed frame part and a lid part movably disposed in the fixed frame part, moving relative to the fixed frame part with the aid of gravity or with the aid of expansion members disposed in the link points between said two parts, whereby sealings are arranged in the moving lid part, with which the suction box is sealed against the inner face of the shell of the suction roll.
In paper and board machines, suction rolls are used in a number of different positions, said rolls being provided with one or more suction boxes. The suction boxes are in such cases sealed against the inner face of the shell of the suction roll with the aid of axial sealings. Said sealings are in general loaded with expansion members against the inner face of the shell of the suction roll, whereby the force directed at the sealings of the expansion members exerts an influence on the wear of the sealings.
A great number of diverse designs are available in the state of art, wherewith endeavors are made to reduce the wear of the suction box sealings. Some said state-of-the-art designs are described below.
In Finnish Patent application No. FI 980759, a sealing structure for the suction box of a suction roll is disclosed. The suction roll comprises a suction box and an elongated capsule-resembling holder part moving in radial direction to the suction roll. The holder part is provided, at a space from each other, with axial sealings disposed in the grooves of the holder part to seal against the inner face of the shell. Between the sealings a suction sector is formed, wherefrom a connection is provided through the holder part to the suction box. The holder part is at both ends fastened on the stationary shaft of the roll with screw means through the aid of which the distance of the holder part can be regulated off from the inner face of the roll shell. With a structure like this, the holder part is prevented from bending along with the shaft of the roll, whereby the axial sealings in the grooves of the holder part, extending across the longitudinal direction of the roll, are at all times kept at a constant distance from the inner face of the shell of the roll. Between the holder part and the suction box, also an actuator such as a piston-cylinder construction can be used, approximately in the middle part of the axial direction of the roll, with which, pushing or traction loading can be directed at the middle part of the holder for bending the holder part into a desired arc.
In Finnish Patent application No. FI 974023, a second sealing structure for the suction box of a suction roll is disclosed. The suction structure comprises a U-shaped holder and a sealing disposed therein, and at least one holder for a loading hose between the bottom wall and the sealing. With a pressure medium conducted into the loading hose, the sealing in the holder can be pressed against the inner face of the suction roll. One side face of the sealing is provided with a cavity with a slanted upper and lower wall, into which a second loading hose is arranged.
Between the loading hose and the side wall of the holder, a piston part is mounted, being equally provided with slanted upper and lower faces. On the opposite side face of the sealing, a second cavity is placed, provided with a slanted upper and lower wall, and with a double section in the bottom part, so that an elongated sealing strip is fitted in both sections of the cavity. A lath is mounted between the sealing strips and a side wall of the holder, being in equal manner provided with slanted upper and lower faces. When pressure medium is conducted into the second loading hose, the sealing is locked onto the side walls of the holder by means of the piston part and the lath. With the first loading hose, the sealing is taken onto the inner face of the roll shell, and with the second loading hose, the sealing is locked onto the side walls of the holder. Owing to the slanted upper and lower walls of the cavities and the likewise slanted upper and lower faces of the piston part and the lath, the sealing moves slightly aside and off from the inner face of the shell of the roll, while the sealing is locked with the second loading hose onto the side faces of the holder.
In Finnish Patent application No. 934909, a third sealing structure for the suction box of a suction roll is disclosed. The sealing structure comprises a holder, being substantially of U-shape and divided into two parts with a third short claw in the middle of the letter U. A sealing is provided in the holder, in the groove in the bottom of which a third claw is disposed. On both sides of the short claw in the middle of the holder bottom, loading hoses are arranged, with the aid of which the sealing can be loaded against the inner face of the shell of the roll. On one side wall of the holder, a cavity is located, on the bottom whereof being provided a third loading hose. Between the third loading hose and the sealing, a locking piston is arranged, with the aid of which the sealing can be locked to the holder. Also on the opposite side wall of the holder, a second locking piston can be provided, so that the sealing is locked with a loading hose between the opposite pistons. The upper faces of the cavities in the side walls of the holder can be slanted similar to the upper faces of the locking pistons, whereby the locking of the sealing to the holder simultaneously releases the sealing off from the inner face of the roll.
The invention can be applied in connection with such suction rolls in which the suction box is formed from a fixed frame part and a moving lid part disposed in the fixed frame part. The moving lid part is provided with holders, whereto axial sealings are attached, to seal against the inner face of the shell of the suction roll and to limit one or several suction sectors. The movement between the fixed frame part and the moving lid part of the suction box is in general achieved in arrangements such as this using expansion members disposed in the link points between the fixed frame part and the moving lid part. By conducting a pressure medium into the expansion members, the space of the moving lid part from the fixed frame part of the suction box can be increased. The movement of the moving lid part is limited with locking nuts, wherewith the metal parts of the holders of the moving lid part are prevented from touching the inner face of the rotary shell of the suction roll in a situation in which the sealings fitted in the holders have worn out. The locking nuts limiting the movement of the moving lid part are adjusted when maintaining the roll.
In such arrangements, the moving lid part cannot be locked in intermediate positions, instead, the expansion members load the moving lid part constantly and therethrough, also the sealings therein against the inner face of the shell, whereby the sealings wear out rapidly and uncontrollably. The wear of the sealings is especially problematic in roll positions in which the lid structure is downwards. Thereby, the moving lid part presses the sealings with its gravity against the inner face of the shell constantly.
The objective of the invention is to solve the problem related to said rapid and uncontrolled wear of the sealings in suction boxes which are formed from a fixed frame part and a lid part movingly positioned in the fixed frame part.
With the arrangement of the present invention, a situation is created in which the moving lid part of a suction box can be locked in a desired spot at each moment, so that the wear of the sealings can be reduced essentially. With the expansion members placed between the link points of the fixed frame part and the moving lid part of the suction box, the axial sealings in the holders of the moving lid part are taken onto the inner face of the shell of the suction roll. Thereafter, the moving lid part is moved slightly towards the fixed frame part with the locking members at the same time as the locking members lock the moving lid part to the fixed frame part. Thus, a situation is created with the locking members, in which the sealings are about to touch the inner face of the shell of the suction roll. When the sealings later wear so that between the sealings and the inner face of the shell of the suction roll a gap is formed which is too wide, the locking can be released, whereafter the sealings are driven with the expansion members again to be attached to the inner face of the shell of the suction roll, whereafter the locking of the moving lid part is carried out again in a new spot.
The arrangement of the present invention functions equally well irrespective of the fact whether the suction roll is in a position in which the lid structure of the suction box is upwards or in a position in which the lid structure of the suction box is downwards. When the lid structure of the suction box is downwards, no expansion members are necessarily needed between the fixed frame part and the moving lid part of the suction box. In said position, the gravity moves the moving lid part downwards, whereby the sealings are pressed against the inner face of the shell of the suction roll.
The invention is described below in detail, reference being made to the embodiment examples of the invention depicted in the figures of the accompanying drawing, whereto the invention is not, however, intended to be exclusively restricted